Deleción subtelomérica 9qter: definición del síndrome y origen parental en 2 pacientes

[Chromosomal location of submicroscopic duplications in patients with neurodevelopmental disorders to identify cases with high risk of familial recurrence]

BACKGROUND AND OBJECTIVE

An important proportion of neurodevelopmental disorders (NDDs) results from unbalanced genomic alterations (duplication or deletion). These chromosomal rearrangements may be considered as de novo, despite they arise as a result of a balanced rearrangement not detected in a phenotypically normal parent. Therefore, if the rearrangements are inherited, the recurrence risk and the genetic counseling of these cases change radically. Fluorescence in situ hybridization (FISH) is a technique that allows detecting both balanced and unbalanced rearrangements, identifying also the location of duplicated segments. We tried to locate in the genome the duplicated segments detected in patients with NDDs in order to identify those cases due to inherited rearrangements.

PATIENTS AND METHOD

The study was conducted in 13 patients with NDDs and genomic duplications detected by compared genomic hybridization-array (CGH-array). Two approaches of FISH technique were taken: hybridization with painting chromosome probes and with specific probes for each duplication.

RESULTS

In the studied series of 13 patients with duplication, 11 patients were found to carry tandem duplications, one with an intrachromosomal insertional translocation, and another with an interchromosomal insertional translocation. Therefore, 2 of the duplications considered de novo were actually an unbalanced rearrangement inherited from a parent who is a balanced carrier.

CONCLUSION

The results illustrate the need to characterize by FISH technique the rearrangements that are detected by CGH-array to identify those cases with a high risk of recurrence.

Maternal isodisomy for chromosome 9 causing homozygosity for a novel FOXE1 mutation in syndromic congenital hypothyroidism

CONTEXT

Homozygous loss-of-function mutations in forkhead box E1/thyroid transcription factor 2 (FOXE1/TTF-2) cause syndromic congenital hypothyroidism, with thyroid dysgenesis, cleft palate, spiky hair, and variable choanal atresia and bifid epiglottis in three cases reported hitherto. We have elucidated the molecular basis of the disorder in a female with a similar clinical phenotype, born to nonconsanguineous parents.

OBJECTIVE AND DESIGN

The FOXE1 gene, located on chromosome 9q22, was sequenced in the proband and family members. Microsatellite marker and multiplex ligation probe amplification analyses determined chromosomal inheritance patterns and FOXE1 copy number. Mutant FOXE1 function was predicted by structural modeling and tested in transfection assays.

RESULTS

The proband was homozygous for a novel missense (c.412T-->C; F137S) FOXE1 mutation, but her mother showed heterozygous and father wild-type alleles for this gene sequence. However, the proband was also homozygous for 10 microsatellite markers spanning chromosome 9 with exclusively maternal inheritance. Multiplex ligation probe amplification assays showed two copies of FOXE1 in the proband, indicating maternal isodisomy for chromosome 9. Consistent with structural modeling, the F137S mutant FOXE1 protein failed to bind DNA and showed negligible transcriptional activity.

CONCLUSION

We have described the first case of uniparental disomy causing homozygosity for a novel, loss-of-function FOXE1/TTF-2 mutation in dysgenetic congenital hypothyroidism.

Is gene discovery research or diagnosis?

The criteria that distinguish human genetic research from clinical molecular diagnosis are frequently practical rather than theoretical. They are driven by the availability and costs of the relevant technologies and the systemic level of scientific fluency in interpreting laboratory results. The guiding principle in the practice of medicine is the primacy of patient care. In the service of this overarching goal the defining characteristic of clinical diagnosis is the definition of the disease entity, even when no immediate treatment is possible. For heritable disorders caused by single-gene defects, identifying the putative causal variant is the goal of molecular diagnostics. Current technologies, costs, and standards of institutional infrastructure have not typically permitted novel gene discovery to be performed within the realm of the clinical laboratory. Discovery is usually funded by self-defined research organizations and carried out by self-defined research personnel with the primary intent of publishing findings in research journals. However, exponential improvements in technological capabilities and the concurrent decline in associated costs seem poised to recast this landscape, bringing to clinical medicine some activities now considered research. Even whole genome resequencing of individual patient DNA is within clinical reach in the foreseeable future.